Semiconductor substrates having useful and transfer layers

ABSTRACT

A semiconductor substrate that includes a relatively thin monocrystalline useful layer, an intermediate layer transferred from a source substrate, and a relatively thick layer of a support present on one of the useful layer of the intermediate layer. The support is made of a deposited material that has a lower quality than that of one or both of the intermediate and useful layers. A bonding layer may be included on one of the intermediate layer or the useful layer, or both, to facilitate bonding of the layers an a thin layer may be provided between the useful layer and intermediate layer. These final substrates are useful in optic, electronic, or optoelectronic applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/009,138filed Dec. 13, 2004, which is a divisional of application Ser. No.10/446,604 filed May 27, 2003, now U.S. Pat. No. 6,867,067, which is acontinuation of International Application PCT/FR01/03715 filed Nov. 26,2001, the entire content of each of which is expressly incorporatedherein by reference thereto.

BACKGROUND ART

The invention relates to methods of fabricating substrates, inparticular for optics, electronics, or optoelectronics, and also tosubstrates obtained by such methods. More particularly, the substratescan be used to make microsystems, sensors, light-emitting or laserdiodes, and the like.

U.S. Pat. No. 5,374,564 discloses a method of fabricating substrates inwhich a thin layer of a material is transferred from a source substrateonto a support. The operation of bonding the thin layer to the supportis often achieved by molecular adhesion, and in order to obtain a goodadhesive interface the surfaces that are to be bonded together must bespecially prepared prior to being brought into contact. Such preparationgenerally includes polishing, planarizing, physical-chemical treatment,fabrication of intermediate layers, and the like, which can berelatively lengthy and complex. This is particularly true when thesupporting substrate is polycrystalline.

Thus, improvements in such substrate preparation methods are desired,and certain new and useful methods are provided by the presentinvention.

SUMMARY OF THE INVENTION

New and useful methods for fabricating final substrates for use inoptics, electronics, or optoelectronics are described. The substratesproduced by these methods are also novel.

In one embodiment, the invention relates to a semiconductor substratecomprising a relatively thin monocrystalline useful layer and arelatively thick layer of a support present on the useful layer.Advantageously, the support is made of a deposited material that has alower quality than that of one or both of the intermediate and usefullayers.

The useful layer is generally made of a material having a large bandgap, such as a material made of compounds of at least two elementsincluding at least one element of aluminum, indium, and gallium.

The support material is typically made at least one of a monocrystallinematerial, a polycrystalline material, an amorphous material, a materialcomprising a plurality of phases, or a material that are less expensivethan that of the intermediate layer.

In another embodiment, a thin layer, transferred from a sourcesubstrate, is provided on one side of the useful layer. This thin layermay be at least one of silicon (1,1,1,), silicon carbide, amonocrystalline material, sapphire, diamond, gallium nitride, aluminumnitride, or a combination of at least two of these materials.

In yet another embodiment, a bonding layer is included on one of thethin layer or the useful layer, or both, to facilitate bonding of thelayers. This bonding layer may be made of at least one of amorphousmaterials, polycrystalline materials, and metallic materials.

Preferred combinations of layers in the substrates are provided by theexamples.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Other aspects, modifications, and advantages of the invention willappear on reading the following detailed description, and the inventionwill also be better understood with the help of the accompanyingdrawings, wherein:

FIG. 1 is a diagram showing the steps in an implementation of the methodin accordance with the invention;

FIG. 2 is a diagram of the steps in another implementation of the methodin accordance with the invention;

FIG. 3 is a diagram of the steps in yet another implementation of themethod in accordance with the invention;

FIG. 4 is a diagram of the steps in yet another implementation of themethod in accordance with the invention;

FIG. 5 is a diagram of the steps in yet another implementation of themethod in accordance with the invention;

FIG. 6 is a diagram of the steps in yet another implementation of themethod in accordance with the invention;

FIG. 7 is a diagrammatic perspective view of an intermediate supporthaving four thin layers that can be used in a variant of the method ofthe invention; and

FIGS. 8 a and 8 b are sectional views showing examples of substratesobtained in a variant of the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides new ways for fabricating final substrates for usein the fields of optics, electronics, or optoelectronics. In particular,substrates having a thin useful layer carried by a mechanical supportmaterial or support layer are made. The method is significantly simplerin comparison to conventional methods and thus is much less expensive touse.

One embodiment of this method includes detaching a thin layer ortransfer layer of material from a source substrate, and then depositinga thick layer of support material onto the thin layer to form amechanical support layer. This method is simple to implement and itenables the omission of lengthy and expensive preparation procedures forthe surfaces that are to be brought into contact, such as polishing,planarizing, and making intermediate layers. All of these steps canoptionally be replaced merely by etching prior to forming the thicklayer, which formation can advantageously be followed or accompanied bya high temperature treatment.

In particular, existing techniques for transferring a thin layer onto athick support (and regardless of whether the thin layer ismonocrystalline, polycrystalline, amorphous, etc.) transfer a thin layeras a single piece onto a previously-prepared thick support. In contrast,the present method forms the thick support directly onto the thin layer.Thus, implementing the present method gives rise to substantial savingsbecause lengthy and expensive surface preparation steps are omitted.

The support material is advantageously deposited directly onto thetransfer layer, for example, by using chemical vapor deposition (CVD).Under such circumstances, the interface obtained between the transferlayer and the support material is of excellent quality, particularly interms of electrical and/or thermal conductivity, which is not generallythe case when conventional methods are used. The support material is arelatively thick layer, and can also be formed by depositing metal, suchas by an electrolytic deposit of copper. In addition, the thick supportmaterial layer can equally be well formed from a material that ismolten, viscous or sintered. The skilled artisan can select the best wayfor forming the support material depending upon the specific use of thefinal substrate.

The method is advantageously implemented for making substrates in whichthe thin transfer layer and the thick support material layer are made ofmaterials possessing close or identical coefficients of thermalexpansion and/or crystal lattice parameters. The method is alsoparticularly advantageous in the context of making composite substratescomprising a monocrystalline thin layer, such as a semiconductormaterial, on a support substrate that is polycrystalline, amorphous,ceramic, or multiphase. Certain techniques, in particular certaindeposition and/or growth techniques, enable thick support materiallayers to be formed at low cost. For example, forming a thick layer ofamorphous or polycrystalline silicon carbide on a thin layer ofmonocrystalline silicon carbide according to the present method makes itpossible to form silicon carbide substrates at a lower cost than if thesubstrate were to be made completely out of a high qualitymonocrystalline silicon carbide.

Furthermore, the present method has the advantage of encouraging goodquality growth of the support material. Thus, when it is desirable tomake substrates at lower cost, conventional methods teach to transfer athin monocrystalline layer onto an inexpensive support material such aspolycrystalline or amorphous material. Regarding the present method, athick layer of inexpensive material may be formed on the thin layer of amaterial having high added value. However, if the thin layer is itselfmonocrystalline, then the thick layer will be of better quality than itwould have been if a one-piece layer of the same material as the thicklayer had been transferred directly onto the thin layer. If the thicksupport material layer formed by the present method is polycrystalline,then better cohesion and better orientation of the various grains areobtained within that material, as is growth of privileged phases.However, this advantage can be diminished if the present method includesforming an intermediate layer, such as an amorphous insulator, betweenthe thin layer and the support.

Under certain conditions, when the thick support material layer is grownon the thin transfer layer according to the present method, the thinlayer serves as a seed layer for monocrystalline orquasi-monocrystalline growth of the thick support layer. Theseconditions correspond to the thick layer being grown epitaxially orquasi-epitaxially on the thin transfer layer. It should be understoodthat the method according to the invention can advantageously includecombinations of the following aspects.

The method may include depositing a useful layer on one or both faces ofthe thin transfer layer. For example, the useful layer can be a materialhaving a large band gap, such as gallium nitride, aluminum nitride, oranother such material, e.g. a compound of at least two elements such asaluminum, indium, and gallium. At least one useful layer may bedeposited before the thick support material layer is formed, or at leastone useful layer may be deposited after the support material has beendeposited. The useful layer and the thick support layer could each bedeposited on a different face of the thin transfer layer. The thintransfer layer could be made of a monocrystalline material.

The support layer could be formed by depositing monocrystallinematerials, polycrystalline materials, amorphous materials, materialscomprising a plurality of phases, or materials that are less expensivethan the material of the thin layer. A skilled artisan can select theoptimum method to use based upon the intended use of the finalsubstrate.

The present method could also include forming a bonding layer on thetransfer layer, the bonding layer being made of amorphous materials,polycrystalline materials, metallic materials such as tungsten, orcombinations of materials such as tungsten silicate. These propertiescan be combined (e.g. polycrystalline and metallic) if desired, and thebonding layer is preferably formed before the thin transfer layer isdetached from the source substrate. The method may also includes a stepof transferring the thin transfer layer onto an intermediate supportprior to forming the thick support material layer on the transfer layer,and then eliminating the intermediate support if desired. Theintermediate support may be eliminated by separating the transfer layerfrom the intermediate layer, and the intermediate layer can then berecycled.

The method can also include forming a bonding layer on the intermediatesupport before transferring the thin transfer layer thereon, the bondinglayer being made of a material such as amorphous materials,polycrystalline materials, and metallic materials, for example, tungstenor tungsten silicate. It should be understood that these materials canbe combined (for example, polycrystalline and metallic). The thintransfer layer may be preferably made of silicon, silicon carbide,sapphire, diamond, gallium nitride, aluminum nitride, or a combinationof at least two of these materials. The thick support material layer maybe preferably formed of silicon, silicon carbide, diamond, sapphire,graphite, gallium nitride, aluminum nitride, boron nitride, or acombination of at least two of these materials.

The thin layer may be detached from the source substrate via a zone ofweakness. The zone of weakness is preferably made by implanting atomicspecies beneath the surface of the source substrate to a predetermineddepth. The thin layer could also be detached from the source substrateby elimination, such as by chemically etching a zone between thetransfer layer and the remainder of the source substrate.

Conditions for depositing the support material may be optimized so thatthe thick support material layer has a particular quality, such as goodmonocrystalline, polycrystalline, insulating, and conductive qualities.It should be understood that the support material may have two or moreof these qualities, such as the good monocrystalline and conductivequalities.

In this document, the term “atomic implantation” covers all types ofbombardment with atomic or ionic species suitable for causing thespecies to be introduced into a material so as to obtain a maximumconcentration of the species in the material. The maximum concentrationmay be situated at a predetermined depth relative to the bombardedsurface. The atomic or ionic species are introduced into the materialwith energy distributed around a maximum. Atomic species can beimplanted into the material by using an ion beam implanter, an implanterthat operates by immersion in a plasma, and the like. The term “atomicor ionic species” is used to cover an atom in ionized, neutral, ormolecular form, or any molecule in ionic or neutral form, or anycombination of different atoms or molecules in ionic or neutral form.While many different species can be used, hydrogen ions are preferred.

The method of the invention is described below with reference to fivespecific but non-limiting implementations.

In a first implementation shown in FIG. 1, a final substrate 14 includesa thin transfer layer 2 on a thick support material layer 4. The supportmaterial forms a mechanical support for the transfer layer. The finalsubstrate is made by performing the following steps. A layer ofamorphous material and a bonding layer 10 are formed on a surface of asource substrate 6 that is preferably subjected to the implantation ofatomic species. Another bonding layer 11 is formed on a surface of anintermediate support 12 of amorphous material. The method preferablyincludes implanting atomic species at a determined depth in the sourcesubstrate 6 to form a zone of weakness 8, and in step 100, the bondinglayers 10 and 11 are joined. In step 200, the transfer layer 2 isdetached from the source substrate 6 via the zone of weakness 8. In step300, a thick support material layer 4 is deposited on the surface of thetransfer layer 2, and in step 400, the bonding layers 10 and 11 areeliminated to separate the transfer layer 2 from the intermediate layer12.

It should be understood that the steps for forming the bonding layer 10and of implanting atomic species can be performed in the order specifiedabove, or in another order.

The step of implanting atomic species and the step 200 of detaching thethin layer 2 are described in U.S. Pat. No. 5,374,564, for example.

The steps of forming the bonding layers 10 and 11 may correspond toforming a layer of amorphous material using one of the knownconventional methods.

It should be understood that the thin transfer layer 2 can be subjectedto additional processing, prior to depositing the thick support layer 4as shown in step 300, in order to form all or some electroniccomponents. In addition, additional films could be deposited uniformlythereon, by epitaxial growth, or otherwise.

EXAMPLES

A number of non-limiting examples are now presented. The following tablesummarizes examples of materials that can be used for implementing thefirst embodiment described above. TABLE 1 Bonding Intermediate layersThin layer 2 support 12 Supporting thick layer 4 10, 11 Mono SiC PolySiC or Poly SiC or poly AlN or SiO₂ or mono SiC diamond or mono SiCSi₃N₄ of quality inferior to that of the thin layer Mono GaN Poly SiC orPoly SiC or poly AlN or SiO₂ or mono SiC or poly GaN or diamond or Si₃N₄sapphire mono SiC of quality inferior to that of the thin layer {111},Poly Si or mono Poly Si or mono Si of SiO₂ or {100} etc. Si or poly SiCor quality inferior to that of Si₃N₄ mono Si mono SiC the thin layer

In the above table, as in the following tables, the term “mono” means“monocrystalline” and the term “poly” means “polycrystalline”.

Example 1

The first example corresponds to the first row of Table 1.

The first implementation is particularly advantageous for forming asubstrate comprising a thin transfer layer 2 of monocrystalline siliconcarbide on a thick support material layer 4 of polycrystalline siliconcarbide. Silicon carbide is difficult to obtain in single crystal form,even with diameters that are much smaller than those which are commonlyobtained for single silicon crystals. This is due in particular to thefact that crystal-drawing techniques are more complex and expensive formonocrystalline silicon carbide than for monocrystalline silicon. Inaddition, the substrate forming steps are more difficult, more timeconsuming, and more expensive, for monocrystalline silicon carbidebecause of the unfavorable ratio between the hardness and thebrittleness of silicon carbide. The present method is thus particularlyadvantageous for fabricating substrates with thin transfer layers 2 ofsilicon carbide since it enables multiple thin layers 2 to be separatedfrom a source substrate 6, and each of those thin transfer layers 2 canbe transferred to a low cost thick support material layer 4.

Furthermore, silicon carbide is used mainly in high power semiconductordevices. Unfortunately, in such applications, certain very restrictivespecifications limit the selection of suitable support substrates forreceiving the thin layer 2 of silicon carbide. In some circumstances,such applications require the support to have good electrical andthermal conductivity properties. Polycrystalline silicon carbidesatisfies these requirements. In some of its properties, it is veryclose to monocrystalline silicon carbide. For example, it provides agood match in terms of the thermal expansion coefficient and it iscompatible with treatment at temperatures that can be as high as 1600°C. or 1700° C. (temperatures that are required for restarting siliconcarbide epitaxy and for annealing after atomic species have beenimplanted).

Furthermore, the use of polycrystalline silicon carbide requires littlemodification to the techniques used by those who commonly usemonocrystalline silicon carbide. Finally, polycrystalline siliconcarbide has good properties with respect to withstanding chemicalattack.

When making a thin transfer layer 2 of monocrystalline silicon carbideon a thick support material layer 4 of polycrystalline silicon carbide,the bonding layers 10 and 11 are advantageously made of silicon oxide.The thick support layer 4 can be made by chemical vapor deposition(which has the major advantage of being capable of being performed atrelatively low deposition temperatures, i.e. at about 1350° C. forsilicon carbide), by vapor phase epitaxy (VPE) or hydride vapor phaseepitaxy (HVPE), by high temperature chemical vapor deposition (HTCVD),or by other equivalent techniques. The thick support layer 4 can also bemade using techniques derived from those generally implemented formaking single crystals, such as subliming techniques or other techniquesgenerally used in methods for drawing balls. The use of such techniquesis not always good from the point of view of deposition quality (due tolow temperatures, non-uniform conditions, high rates of growth, etc.),but can be advantageous from the point of view of cost.

For silicon carbide substrates having a diameter of about 50 millimeters(mm), the thick support layer 4 is advantageously about 300 microns (μm)thick. The thick support layer 4 of silicon carbide may beadvantageously made by chemical vapor deposition with growth takingplace at a rate of about 100 μm per hour.

Furthermore, by using a monocrystalline material surface of the thintransfer layer 2 for depositing 300 the thick support layer 4,deposition parameters can be optimized so as to produce amonocrystalline support substrate. The thin transfer layer 2 can thusserve as a seed layer for growing a monocrystalline thick supportmaterial layer 4. Depending on the degree of optimization of thedeposition parameters and depending on the intended application, thismonocrystalline thick support layer 4 can be of poor or of mediumquality, but the resulting substrate will nevertheless present theadvantage of being of relatively low cost. However, it is also possiblefor the monocrystalline thick support layer 4 to be of good or of verygood quality if required. The thick support layer 4 can be grown to forma substrate with a layer 4 that is very thick, for example, that is agreat deal thicker than a few hundreds of micrometers, depending on theapplication. In variants of the implementation described above, thethick support layer 4 can be made not only of silicon carbide, but ofpolycrystalline aluminum nitride, of diamond, or of other materials.

The intermediate support 12 must be capable of withstanding conditionsin which the thick support layer 4 of silicon carbide is grown, and mustalso be capable of being eliminated. The technique selected for removingthe intermediate support 12 can also help to select the material used tomake it. If it is to be removed by etching or by mechanical or chemicalremoval, then the etching and removal steps, and also the intermediatesupport 12 must be of low cost. In such a situation, it is advantageousto use aluminum nitride. Low cost silicon can also be used, but it ismore difficult to make silicon compatible with the silicon carbide ofthe thick support layer 4. In contrast, if the intermediate support 12is removed and recovered, then it is possible to use materials that aremore expensive. Under such circumstances, it is possible to selectpolycrystalline silicon carbide, or possibly monocrystalline siliconcarbide since it can be reused.

Advantageously, an intermediate support 12 is used made ofpolycrystalline silicon carbide covered in a bonding layer 11 of siliconoxide. The use of silicon oxide makes it easier to remove the thintransfer layer 2 from the source substrate 6. Planarized deposition ofsilicon oxide makes it possible to eliminate any surface irregularitiesand to perform polishing, planarizing, cleaning, chemical preparation,and bonding silicon oxide on silicon oxide operations by usingtechniques that are known and easy to implement.

The silicon oxide material of the bonding layers 10 and 11 can also bereplaced by some other material, for example silicon nitride (Si₃N₄).This material can withstand higher temperatures than silicon oxide,which makes it particularly suitable for optimizing the deposition of athick support layer 4 for the purpose of forming a high qualitymonocrystalline or polycrystalline layer, or when an increased rate ofdeposition is desired.

This first example of an implementation of the present method includesmaking a multi-layer structure, or stack, having a thin transfer layer 2of monocrystalline silicon carbide, two bonding layers 10 and 11 ofsilicon oxide, and an intermediate support 12 of polycrystalline ormonocrystalline silicon carbide. This structure can be made by a layertransfer method known to the person skilled in the art (e.g. anapplication of a SMART-CUT® method of the kind described in U.S. Pat.No. 5,374,564). Referring to FIG. 1, the method also includes, in step300, depositing a thick support layer 4 of silicon carbide, for example,by CVD at 1350° C. onto the free surface of the thin transfer layer 2.Then, in step 400, the bonding layers 10 and 11 are eliminated bychemical etching in a bath of hydrofluoric acid, and the intermediatesupport layer 12 is recovered. The silicon carbide can be inpolycrystalline or monocrystalline form and is inert in hydrofluoricacid, whereas silicon oxide etches very easily in this substance.Lastly; the surface of the polycrystalline silicon carbide thick layer 4can undergo a final rough polishing, because rough polishing issufficient since the thick support layer 4 becomes the rear support faceof the final substrate 14. Under certain conditions the thick supportlayer 4 is deposited in a controlled manner so that this final polishingstep can be omitted.

If necessary, the geometrical shape of the final substrate 14 may bemodified to ensure that the final substrate 14 has the desired diameter,or to shape the way its sides drop, or to eliminate nodules from theedges of the substrate, and the like. In addition, the front face of thesilicon carbide single crystal of the final substrate 14, which is thefree surface of the thin layer 2, can advantageously be protected duringfinishing operations. In particular, the front face may be protectedduring any optional polishing operation of the rear face of the finalsubstrate 14. It should be noted that during the initial steps of themethod, the thin transfer layer 2 is naturally protected by theintermediate support 12.

The final substrate 14 obtained by the above-described implementationpresents an interface between the thin transfer layer 2 and the thicksupport layer 4 which is highly conductive, both electrically andthermally. This occurs because the material of the thick support layer 4is deposited directly onto the thin layer 2, making it possible to avoidthe voids that would otherwise be formed during bonding which occurswhen using conventional methods. In addition, unlike prior arttechniques, there are no intermediate layers of silicon oxide or otherlike materials that are generally used in adhesive techniques. Thepresent method also makes it possible to omit the steps of planarizingand polishing the silicon carbide, which is a very hard and chemicallyinert material. This is particularly advantageous since detrimentalpolishing problems may occur when using polycrystalline silicon carbidesince the rates of attack during polishing vary between grains, orbetween grains and grain boundaries, and also may vary as a function ofthe intrinsic and bulk crystal quality of the grains.

Nevertheless, it should be observed that in certain applications, themethod can be implemented to form a thick support layer 4 in which theselected materials or conditions of implementation result in aninterface which is a poor conductor of electricity or heat. This canoccur by using an intermediate layer of insulating material between thethin transfer layer 2 and the thick support layer 4.

The first implementation of the present method can be the subject ofnumerous variants. In particular, other materials can be substituted,such as those listed by way of example in the first row of Table 1. Inthis first implementation, it is also possible to substitute the step400 of chemically etching the bonding layers 10 and 11 for an operationinvolving separating the intermediate support 12 and the thin transferlayer 2. For example, if the intermediate support 12 has undergone aprior operation of implanting atomic species therein, then a mechanicalstress can be applied to cause the separation. Other techniques forfacilitating the step 400 to eliminate the bonding layers 10 and 11and/or to separate the intermediate support 12 from the thin layer 2could be used, such as by forming channels in the bonding layers 10 and11.

It is also possible to implement the present method without using anintermediate support 12. This applies transferred thin layer 2 issufficiently thick and is made of a material that is sufficientlystrong. For example, a thin layer 2 of silicon carbide having athickness of about a few tens of microns can have sufficient mechanicalstrength.

It should also be observed that the polarity of the thin transfer layer2 of silicon carbide taken from the source substrate 6 can be selectedas a function of the polarity of the initial source substrate 6. Thepolarity of a silicon carbide substrate corresponds to the Si face or tothe C face and is a concept which is well known to the person skilled inthe art. It is possible to take the thin layer 2 from the sourcesubstrate 6 by applying two transfer operations thus making it possibleto change polarity twice.

It is also possible to form an intermediate layer, like an insulatinglayer, on the thin transfer layer 2 before depositing the thick supportlayer 4. For example, the intermediate layer can be a fine oxide (500angstroms (Å) thick). This provides, for example, an SiC substrate oninsulation, made up of a thin layer 2 of SiC on a fine intermediatelayer of silicon oxide, with both layers then being located on a thicklayer 4 of polycrystalline silicon.

A second example of the first implementation is described below. In thisexample, the operation corresponds to making a substrate of galliumnitride, for optoelectronic applications in particular.

Example 2

This second example corresponds to the second line of Table 1, andcomprises the steps shown in FIG. 2. The operation includes depositing athin layer 2 of monocrystalline gallium nitride on a source substrate 6of monocrystalline silicon carbide by metal organic chemical vapordeposition (MOCVD) or by molecular beam epitaxy (MBE). A bonding layer10 of silicon oxide is deposited on the thin layer 2, and a bondinglayer 11 of silicon oxide is deposited on an intermediate support 12 ofpolycrystalline silicon carbide. Next, in step 100, the two bondinglayers 10 and 11 are placed in contact with each other, and bondedtogether. The method includes, in step 200, detaching the thin layer 2of gallium nitride from the source substrate 6 via the interface betweenthe thin transfer layer 2 and the source substrate 6 (e.g. by applyingmechanical stresses) or via a zone of weakness made, for example, byimplanting atomic species in the monocrystalline silicon carbide of thesource substrate 6 or in the gallium nitride of the thin layer 2. Next,in step 300, a thick support layer 4 of polycrystalline silicon carbideis deposited by CVD onto the free surface of the thin layer 2, and instep 400, the intermediate support is separated by eliminating thebonding layers 10 and 11, e.g. in a bath of hydrofluoric acid or merelyby removing material (by eliminating the intermediate support 12 and thebonding layers 10 and 11 using the so-called “Etch-back” technique) orby fracturing the bonding layers 10 and 11 via a pre-weakened zone orotherwise, or by using any other technique known to the person skilledto enable a substrate to be separated into two portions in apredetermined zoned by applying a mechanical, thermal, chemical,electrostatic, or other type of stress.

Other variants of Example 2 are contemplated. Thus, the operation 300 ofdepositing polycrystalline silicon carbide can be replaced by chemicalvapor deposition of polycrystalline aluminum nitride or polycrystallinegallium nitride, or by forming a diamond layer in order to form thethick support layer 4. In another variant, the polycrystalline galliumnitride of the thick support layer 4 is formed by high pressure VPE. Inyet another variant, the polycrystalline silicon carbide of theintermediate support 12 is replaced by aluminum nitride or sapphire; athick support layer 4 of polycrystalline aluminum nitride can then bedeposited 300 by CVD prior to eliminating 400 the bonding layers 10 and11. In yet another variant, the method is the same as in one of thevariants describe with reference to Example 2, except that a final thintransfer layer 2 is made of not only gallium nitride, but also a layerof the underlying silicon carbide of the source substrate 6. This can bedone by forming a weak layer at a certain depth in the source substrate6, for example, by implanting atomic species. In such a case, in yetanother variant, not only are the bonding layers 10 and 11 eliminated,but the portion of the thin transfer layer 2 that is made of siliconcarbide is also eliminated if two transfers are performed on the thintransfer layer 2, such that an extra transfer occurs before placing iton the intermediate support 12.

In yet other variants, the layer of gallium nitride making up the thintransfer layer 2 is replaced by aluminum nitride or some other material,or by a stack of different materials, possibly together with otherintermediate compounds.

Example 3

A third example of the first implementation is described below.

This example corresponds to making monocrystalline silicon substrates oflarge diameter. These substrates are expensive since they are difficultto make. As for monocrystalline silicon carbide substrates, it isadvantageous to make a thin layer of monocrystalline material on asupport material of poorer quality, for example of a material that ispolycrystalline, amorphous, or otherwise. If the thin transfer layer isbonded directly onto a support, then difficulties will arise concerningpolishing, planarizing, physical-chemical operations at the adhesiveinterface, degassing, and the like. The present method advantageouslymakes it possible to avoid such difficulties, since the support is madeby directly depositing a thick support layer 4 on one of the faces ofthe thin transfer layer 2.

As mentioned above, the method of the invention makes it possible toprovide an interface of very good quality.

Advantageously, doping is performed, possibly varying as a function ofdepth while the thick layer 4 is being deposited to enhance theelectrical and thermal transparency of the interface.

The third example corresponds to the third row of Table 1. A thintransfer layer 2 of monocrystalline silicon is made on insulation(bonding layer 10 and/or 11), on an intermediate support 12. Next, athick support layer 4 of polycrystalline silicon is formed 300 on thethin transfer layer 2 so as to have a thickness of at least 725 μm. Instep 400, the intermediate support 12 is separated and recovered. Aphysical-chemical treatment is performed by selective etching ofsilicon/silicon oxide (e.g. using hydrofluoric acid) and/or mechanicalremoval operations are performed so as to ensure that the surface zoneof the silicon in the thin layer 2 is of good quality. Lastly, formingoperations are performed with attention to the planar quality, thethickness, the edges, and the like (which may include polishing,lapping, shaping the edges, chemical treatment of the final substrate 14in order to make it comply with standards such as SEMI or JEIDA, forexample).

As already described above, the step of making a substrate of silicon oninsulation can be performed by implanting atomic species to create azone of weakness 8 in a silicon source substrate 6. Then a silicon oxidebonding layer 10 is formed on the source substrate 6, and anothersilicon oxide bonding layer 11 is formed on the intermediate support 12of silicon which can be polycrystalline or even monocrystalline. Thenthe bonding layers 10 and 11 are joined to bond them together prior todetaching the thin transfer layer 2 from the source substrate 6. Thisstep of making a substrate of silicon on insulation can be performed bya SMART-CUT® technique, for example (see U.S. Pat. No. 5,374,564, forexample).

After the thick support layer 4 has been formed, the silicon oninsulation substrate must be removed. Removal can be done using anyknown technique suitable for detaching the thin transfer layer 2 ofsilicon from the source substrate 6. One such technique is known as the“lift-off” technique, whereby the buried silicon oxide is eliminated(e.g. the bonding layers 10 and 11). Another technique can make use ofmechanical stress. Instead of using the above-mentioned lift-offtechnique, it is also possible to use mechanical, thermal,electrostatic, and/or other stresses to separate the two parts situatedon either side of an adhesive interface, an epitaxial interface, aporous zone, or a pre-weakened zone, for example.

The intermediate support 12 can be separated via the first adhesiveinterface or via any one of the adhesive interfaces between the bondinglayers 10 and 11 and the intermediate support 12. If an additional stepof implanting atomic species (e.g. hydrogen) is performed, separationmay occur in the bonding layers 10 and 11, in the thin transfer layer 2,or in the intermediate support 12 via the weakened zone.

It will be observed that the above-mentioned forming operations can alsobe implemented in part or in full prior to separating the thin transferlayer 2 from the intermediate support 12.

It should also be observed that prior to the step 300 of depositing thethick layer 4, insulation (such as an oxide, nitride, diamond and thelike) can be formed on the thin layer 2 so that the final substrate 14has a silicon on insulation structure. In a variant of the exampledescribed above, a thick layer 4 of diamond is formed on the thin layer2. The resulting final substrate 14 is particularly advantageous when itis necessary to have good heat removal of any heat generated within thethin transfer layer 2.

A second implementation of the present method is shown in FIG. 3. A thinlayer 2 is formed on a thick layer 4 in the manner described above forthe first implementation, and then a useful layer 16 is deposited on thefree face of the thin transfer layer 2.

Table 2 below summarizes six examples of this second embodiment of thepresent method in the context of making substrates of interest in thefields of electronics, optics, or optoelectronics. TABLE 2 Useful layerIntermediate Bonding 16 Thin layer 2 support 12 Thick layer 4 layers 10,11 GaN or AlN or Mono SiC Poly SiC or mono Poly SiC or SiO₂ or Si₃N₄AlGaN or GalnN or SiC (in particular if diamond or other recycled) boronnitride GaN or AlN or {111} Si Poly SiC or mono Poly SiC or SiO₂ orAlGaN or SiC (in particular if diamond or Si₃N₄ GalnN or recycled) boronnitride other GaN or AlN or Sapphire Poly SiC or mono Poly SiC or SiO₂or AlGaN or SiC (in particular if diamond or Si₃N₄ GalnN or recycled)boron nitride other GaN or AlN or Mono SiC or Poly SiC or mono Poly AlNor SiO₂ or AlGaN or {111} Si or SiC (in particular if diamond or Si₃N₄GalnN or sapphire recycled) boron nitride other GaN or AlN or Mono SiCor Poly SiC or mono Poly GaN or SiO₂ or AlGaN or {111} Si or SiC (inparticular if diamond or Si₃N₄ GalnN or sapphire recycled) boron nitrideother GaN or AlN or Mono SiC or Poly AlN AlN or GaN or SiO₂ or AlGaN or{111} Si or poly SiC or Si₃N₄ other sapphire diamond or boron nitride

Example 4

In this example (see the 1st row of Table 2) a thin transfer layer 2 ofmonocrystalline silicon carbide is made on an intermediate support layer12 of polycrystalline silicon carbide with bonding layers 10 and 11 ofsilicon oxide between them. A thick support layer 4 of polycrystallinesilicon carbide is then deposited by CVD. The resulting structure isthen subjected to treatment suitable for detaching the structureincluding the thin layer 2 on the thick layer 4 from the intermediatesupport. For example, such treatment may include etching the bondinglayers 10 and 11 in hydrofluoric acid, with or without adding amechanical stress. Treatment could also merely be removing the materialof the intermediate support 12 and possibly also that of the bondinglayers 10 and 11. Finally, a useful layer 16 of gallium nitride isdeposited on the free face of the monocrystalline silicon carbide of thethin layer 2 by MOCVD. The useful layer 16 of gallium nitride isparticularly suitable for optoelectronic applications.

Example 5

In this example (see second row of Table 2) a structure comprising athin transfer layer 2 of {111} silicon is formed on an intermediatesupport 12 of polycrystalline silicon carbide in the manner describedabove. There is a layer of silicon oxide between them. A thick supportlayer 4 of polycrystalline silicon carbide is deposited on the thintransfer layer 2 of {111} silicon by CVD. The resulting structure isthen subjected to treatment in a bath of hydrofluoric acid, with orwithout mechanical stress, or any other treatment suitable to separatethe thin layer 2 and the thick support material layer 4 from theintermediate support 12. Thereafter MOCVD is used to depositmonocrystalline gallium nitride on the free surface of the {111}silicon, which is a material known for enabling good epitaxy of galliumnitride. The thickness of the {111} silicon is preferably advantageouslylimited to less than about 1000 Å to enable it to accommodate procedureswithout breaking due to thermal expansion that can occur during thevarious operations mentioned above.

Example 6

In this example (see third row of Table 2), a thin transfer layer 2 ofsapphire is made on a polycrystalline silicon carbide intermediatesupport layer 12 having bonding layers 10 and 11 of silicon oxidebetween them. A support material layer 4 of silicon carbide is thendeposited 300 (see FIG. 3) on the thin layer 2. The bonding layers 10and 11 are eliminated to enable the intermediate support 12 to berecovered. Finally, a useful layer 16 of gallium nitride is deposited onthe sapphire. Sapphire is another material that is known for enablinggood epitaxy of gallium nitride.

Example 7

In this seventh example (see fourth row Table 2), one of the structuresdescribed in any one of the three preceding examples is made, but thethick support layer 4 of polycrystalline silicon carbide is replaced bya layer of polycrystalline aluminum nitride.

Example 8

In this example (see fifth row of Table 2), a structure is made of thetype described in any one of Examples 4 to 6 above, but the thicksupport layer 4 of polycrystalline silicon carbide is replaced by alayer of polycrystalline gallium nitride deposited by HVPE.

Example 9

In this example (see sixth row of Table 2) a structure is made asdescribed in any one of the five preceding examples, but in which thepolycrystalline silicon carbide of the intermediate support 12 isreplaced by polycrystalline aluminum nitride.

In examples 3 to 9 above, the monocrystalline silicon carbide, the {111}silicon, or the sapphire is used as a substrate for gallium nitrideepitaxy. The advantage of silicon carbide is that its coefficient ofthermal expansion is similar to that of gallium nitride.

It should be noted that the thickness properties of the thick supportlayer 4 can be important. For example, it may be desirable to make anelectrical contact with the rear face of the final substrate 14, or tovent heat generated by components formed in the useful layer 16, or toextract and control light emitted by a diode or a laser made in theuseful layer 16.

It should also be noted that if the thin transfer layer 2 has a suitablethickness and is sufficiently stiff, then structures equivalent to thosedescribed above can be made without using an intermediate support 12.

Numerous other variants of this second implementation of the method arealso possible. Thus, the step of forming the thick layer 4 ofpolycrystalline SiC, of aluminum nitride, or of gallium nitride, can bereplaced by a step of forming a thick layer 4 of diamond or of boronnitride.

In other variants, the nature of the intermediate support 12 can bedifferent. Thus, monocrystalline silicon carbide can be used (inparticular when it can be recycled), to replace the polycrystallinesilicon carbide or the polycrystalline aluminum nitride.

Similarly, these examples can be changed to reflect a structure, forexample, in which a useful layer 16 of aluminum nitride, of an alloy ofaluminum and gallium, or of an alloy of gallium and indium, and the likeis formed in accordance with the present method instead of the usefullayer 16 of gallium nitride as described above. The useful layer 16 ofgallium nitride can also be a multilayer structure made of a stack oflayers of gallium nitride, aluminum nitride, and such like types, withoptional different kinds of doping, and the like.

A third implementation of the present method is shown in FIG. 4. Astructure is formed in which the thick layer 4 is deposited directly onthe useful layer 16, contrary to the description given above for thesecond implementation of the method. The useful layer 16 is itselfdeposited directly on the thin transfer layer 2 after this layer hasbeen separated from the source substrate 6.

The third implementation of the method of the invention is describedbelow, and the materials used in the context of these three examples aresummarized in Table 3. TABLE 3 Useful layer Intermediate Bonding layers16 Thin layer 2 support 12 Thick layer 4 10, 11 GaN or AlN or Mono SiCor Poly (or mono) AlN or GaN SiO₂ or AlGaN or {111} Si or SiC or polyAlN or poly SiC or Si₃N₄ GalnN or sapphire or diamond or other otherother GaN or AlN or Mono SiC or Poly (or mono) AlN or GaN SiO₂ or AlGaNor {111} Si or SiC or poly AlN or poly SiC or Si₃N₄ GalnN or sapphire +etching or diamond or other other other + etching a Mono SiC or Poly (ormono) AlN or GaN SiO₂ or portion of the {111} Si or SiC or poly AlN orpoly SiC or Si₃N₄ GaN or other sapphire + etching or diamond or otherother

Example 10

In this example (see first row of Table 3) a structure is made thatincludes a thin layer 2 of monocrystalline silicon carbide on anintermediate support 12 of polycrystalline silicon carbide with bondinglayers 10 and 11 of silicon oxide between them. This structure can bemade in the manner described above for the first and secondimplementations. Thereafter, a useful layer 16 of monocrystallinegallium nitride is formed on the free surface of the thin transfer layer2 of silicon carbide by MOCVD. A thick support material 4 ofpolycrystalline silicon carbide is then deposited by CVD on the usefullayer 16. The resulting structure is then subjected to a step 700 oftreatment suitable for separating the structure made of the thintransfer layer 2, the useful layer 16, and the thick support layer 4from the intermediate support 12. For example, the treatment may consistof etching with hydrofluoric acid, with or without mechanical stressbeing applied, or merely by removing matter. This provides a structureor stack that includes a thick support layer 4 that supports a usefullayer 16 of gallium nitride, itself covered by a thin transfer layer 2of monocrystalline silicon carbide. After separation, the intermediatesupport 12 is ready for recycling.

In this case, and unlike the second implementation of the methoddescribed above, the monocrystalline gallium nitride is deposited beforethe thick support layer 4 is formed.

Example 11

In another example of the third implementation, the structure of Example10 is made and then the thin transfer layer 2 of monocrystalline siliconcarbide is withdrawn, for example, by using a step 800 of etching withplasma (see second row of Table 3).

Example 12

In yet another example of this third implementation (see third row ofTable 3), a structure of the kind described in Example 11 is made,except that not only is the transfer layer 2 of monocrystalline siliconcarbide removed, but a portion of the useful layer of gallium nitride isalso removed.

It should be noted that the thin transfer layer 2 of monocrystallinesilicon carbide, or the useful layer 16 of monocrystalline galliumnitride can be subjected to various additional processing steps prior tothe deposit of the support material 4. These steps may produceelectronic components, in full or in part, or they can comprise makinguniform deposits of additional films by epitaxial growth or otherwise.

It should also be noted that the polarity of the thin transfer layer 2of monocrystalline silicon carbide and that of the useful layer 16 ofgallium nitride can be determined by selecting the polarity of theinitial source substrate 6. Optionally, the method can include at leastone double transfer to enable the polarity to be changed twice insuccession.

Similarly, these examples can be changed, for example, to form a usefullayer 16 of aluminum nitride, or an alloy of aluminum and gallium, or ofan alloy of gallium and indium, instead of the gallium nitride usefullayer 16 as described above. The gallium nitride useful layer 16 canalso be made by forming a multilayer structure that includes a stack oflayers including gallium nitride, aluminum nitride, and other types oflayers, possibly with doping of different kinds.

In other variants, the nature of the intermediate support 12 is changed.Thus, monocrystalline silicon carbide is used (in particular when theintermediate support is recycled), or else use is made of diamond orsome other material to replace the polycrystalline silicon carbide orthe aluminum nitride.

In a fourth embodiment of the present method, as shown in FIG. 5, auseful layer 16 is deposited on a thin transfer layer 2 that is locatedon an intermediate support 12. The useful layer is deposited prior toseparating the intermediate support 12 from the structure made of thethin transfer layer 2 and the useful layer 16. The thick support layer 4is then deposited on the thin transfer layer 2, or on the useful layer16. Thus, the support material is deposited on one side or the other ofthe structure that includes the thin transfer layer 2 and the usefullayer 16.

This fourth implementation of the method is illustrated by the followingtwo examples.

Example 13

In this example, the following steps are performed. The method includesforming a structure made up of a thin transfer layer 2 ofmonocrystalline silicon carbide on a source substrate 6 with a zone ofweakness 8, and an intermediate support 12 with bonding layers 10 and 11between them, which is as described above for the first implementation.Next, the technique includes detaching the thin layer 2 from the sourcesubstrate 6 via a zone of weakness 8 (which is obtained by an implantingstep performed in the source substrate 6 prior to being put into contactwith the intermediate support 12). A useful layer 16 of monocrystallinegallium nitride is then deposited on the free surface of the thin layer2 of silicon carbide. The composite substrate made of the thin layer 2and the useful layer 16 is then detached from the intermediate support12 (for example, by treatment in a bath of hydrofluoric acid). Lastly, athick support material layer 4 of polycrystalline silicon carbide isdeposited on the free surface of the useful layer 16.

Example 14

In this example, the procedure is the same as in the preceding example,except that the step of depositing the thick support layer 4 on theuseful layer 16 is replaced by a step of depositing the thick layer 4 onthe thin transfer layer 2.

As mentioned above, if the thickness and the strength of the thin layer2 together with the useful layer 16 are sufficient, then theimplementations described above can be realized without using anintermediate support 12. It may also be possible to realize theimplementations without using an intermediate support 12 whiledepositing the thick support layer 4, but then a temporary support couldbe used which serves as a stiffener. Such a temporary support could beremoved before depositing the thick layer 4.

The fifth implementation corresponds to methods that do not use eitheran intermediate support 12 or a temporary support. Several examples ofsuch implementations that do not include an intermediate support 12 areshown in FIG. 6. In particular, starting from a source substrate 6 inwhich a zone of weakness 8 has been produced (for example, by implantingatomic species), it is possible to separate the thin transfer layer 2 byitself. It is also possible to deposit a useful layer 16 on the thinlayer prior to separating it from the source substrate 6 via the zone ofweakness 8. In the first case, the thick support layer 4 can bedeposited on the thin transfer layer 2 (thus reproducing the finalsubstrate 14 of Example 1, for example). This technique can also becontinued by depositing a useful layer 16 on the opposite face of thethin layer 2 (opposite of the face that received the thick support layer4) to form the final substrate 14 of Example 4, for example. In thesecond case, the thick support layer 4 is deposited on the same side asthe thin transfer layer 2 (thus reproducing the final substrate 14 ofExample 4) or on the same side as the useful layer 16 (thus reproducingthe final substrate 14 of Example 10). Optionally, as described withreference to FIG. 4 (see step 800), it is then possible to remove thethin transfer layer 2 (thus reproducing the final substrate of Example11, for example).

Numerous variants of the implementations described above arecontemplated. For example, the various operations described above in theexamples can be combined.

As shown in FIG. 7, one variant of the method includes batch processingthin transfer layers 2 that have been obtained prior to depositing thethick support material layer 4. Under such circumstances, the thintransfer layers 2 are fixed on a single intermediate support 12 of largesize. It should be noted that the single intermediate support 12 can bean arbitrary shape (circular, rectangular, square, or other shape). Thethin transfer layers 2 can be identical or they can be different. Eachof the thin layers 2 can be subjected to a separate operation ofdetaching the thin transfer layer from the intermediate support 12. Forexample, the single intermediate support 12 can be a plate ofpolycrystalline silicon carbide covered in a silicon oxide. After thethick support material layer 4 has been deposited, the compositesubstrate comprising the single intermediate support 12 and theassociated thin layers 2 and thick support layers 4 can be subjected toa lift-off operation in a bath of hydrofluoric acid. Each individualintermediate support 12 can then be recycled.

In yet another variant of the implementations described above, a thicksupport layer 4 is deposited on a surface that is larger than thesurface corresponding to the main faces of the thin transfer layer 2.This variant is shown in FIG. 8, wherein a structure is made of a thintransfer layer 2 on an intermediate support 12 with bonding layers 10and 11 between them (similar to that made in the first implementationdescribed above). This structure is then placed in a sample carrier 20in such a manner that the free surface of the thin transfer layer 2 isflush with the surface of the sample carrier 20 (see FIG. 8 a). A thicksupport layer 4 is then formed on the free surface and overflows ontothe sample carrier 20.

The substrate formed in this way can optionally be subjected totreatment suitable for eliminating the projecting edges of the thintransfer layer 2. The edges of a deposited layer generally presentirregularities, such as defects, beading, and the like. The presentvariant makes it possible to eliminate such edges. This variant is alsoadvantageous for forming a substrate having a diameter that is greaterthan that of the thin layer 2, and adapted to a line for processingsubstrates of a given diameter, even though the thin layer 2 cannot beformed to have that diameter. This variant is also advantageous when,during formation of a single thick support layer 4 on a plurality ofthin layers 2, a single support is made for a plurality of thin transferlayers 2 and/or useful layers 16 (see FIG. 8 b). This variant can alsobe implemented by forming a thick support material layer 4 on each ofthe assemblies made of an intermediate support 12 and a thin transferlayer 2 and placed on a plane sample carrier. The thick support layer 4then drops back onto the edges of the thin transfer layer 2.

A variant of the method optimizes the parameters for depositing thethick support layer 4 so that the thick layer 4 is formed as a singlecrystal. Even if the quality of such a monocrystalline thick supportlayer 4 is not good, it can be suitable for numerous applications thatrequire very high crystal quality only on the surface of the transferlayer 2 or useful layer 16. Such variants of the method are particularlyadvantageous when it is not possible to grow single crystals (as is thecase for gallium nitride) or when it is expensive to grow singlecrystals (as is the case for monocrystalline silicon carbide).

It is possible to perform chemical vapor deposition of a thick supportlayer 4 of silicon carbide on a surface of layer 2 or 16 which then actsas a seed layer for growing the thick support layer 4, while using veryhigh rates of growth (several tens to several hundreds of microns perhour).

It will be observed that conventional techniques often grow thintransfer layers 2 on a support by epitaxy. Under such circumstances, thesubstrate must be of very good quality so as to ensure that theepitaxially grown thin layer is likewise of very good quality, to ensurethat defects are not transferred.

In contrast, the present method enables the thick support layer 4 to bemade at low cost since it is a support whose quality can often beinferior, particularly since it is not necessarily used for restartingepitaxial growth.

In other variants, the above described methods may be used with othertypes of semiconductors such as indium phosphide and gallium arsenide,or used with other materials such as lithium niobate.

In yet other variants, an intermediate layer, such as an insulatinglayer, can be made between the thin transfer layer 2 and/or the usefullayer 16, and on the thick support layer 4, or between the thin layer 2and the useful layer 16. For example, an intermediate layer can be madeof diamond or of fine oxide (of about 500 Å thick).

1. A semiconductor substrate comprising a relatively thinmonocrystalline useful layer and a relatively thick layer of a supportpresent on the useful layer, wherein the support is made of a depositedmaterial that has a lower quality than that of the useful layer.
 2. Thesubstrate of claim 1, wherein the useful layer is made of a materialhaving a large band gap.
 3. The substrate of claim 1, wherein the usefullayer is made of compounds of at least two elements including at leastone element of aluminum, indium, or gallium.
 4. The substrate of claim1, wherein the useful layer comprises at least one of gallium nitride oraluminum nitride.
 5. The substrate of claim 1, wherein the supportmaterial is at least one of a monocrystalline material, apolycrystalline material, an amorphous material, or a materialcomprising a plurality of phases.
 6. The substrate of claim 1, whereinthe support material is made of at least one of silicon, siliconcarbide, sapphire, diamond, graphite, gallium nitride, aluminum nitride,or a combination of at least two of these materials.
 7. The substrate ofclaim 1, further comprising a thin layer on one side of the usefullayer, optionally wherein the thin layer is transferred from a sourcesubstrate.
 8. The substrate of claim 7, wherein the thin layer is atleast one of silicon (1,1,1,), silicon carbide, a monocrystallinematerial, sapphire, diamond, gallium nitride, aluminum nitride, or acombination of at least two of these materials.
 9. The substrate ofclaim 7, wherein the useful layer is made of a material having a largeband gap.
 10. The substrate of claim 9, wherein the useful layer is madeof compounds of at least two elements including at least one element ofaluminum, indium, or gallium.
 11. The substrate of claim 7, wherein thesupport material is at least one of a monocrystalline material, apolycrystalline material, an amorphous material, or a materialcomprising a plurality of phases.
 12. The substrate of claim 11, whereinthe support material is made of at least one of silicon, siliconcarbide, sapphire, diamond, graphite, gallium nitride, aluminum nitride,or a combination of at least two of these materials.
 13. The substrateof claim 7, further comprising a bonding layer on the useful layer tofacilitate bonding.
 14. The substrate of claim 13, wherein the bondinglayer is made of at least one of amorphous materials, polycrystallinematerials, or metallic materials.
 15. The substrate of claim 13, whereinthe useful layer is SiC, the thin layer is monocrystalline SiC, thesupport material is polycrystalline SiC, polycrystalline AlN, diamond ora monocrystalline SiC of inferior quality to that of the useful layer,and the bonding layer is SiO₂ or Si₃N₄.
 16. The substrate of claim 13,wherein the useful layer is monocrystalline GaN, the thin layer ismonocrystalline SiC, sapphire or silicon, and the support material ispolycrystalline SiC, polycrystalline GaN, polycrystalline AlN, diamondor a monocrystalline SiC of inferior quality to that of the usefullayer, and the bonding layer is SiO₂ or Si₃N₄.
 17. The substrate ofclaim 13, wherein the useful layer is monocrystalline Si(1,1,1,), thethin layer is monocrystalline Si or monocrystalline SiC, the supportmaterial is polycrystalline Si or monocrystalline Si of inferior qualityto that of the useful layer, and the bonding layer is SiO₂ or Si₃N₄.